Abstract
Patchiness of habitat has important influences on distributions and abundances of organisms. Given the increasing threat of loss and alteration of habitats due to pressures associated with humans, there is a need for ecologists to understand species' requirements for habitat and to predict changes to taxa under various future environmental conditions. This study tested hypotheses about the generality of patterns described for one species of marine intertidal turban snail for a different, yet closely-related species in subtidal habitats along the coast of New South Wales, Australia. These two closely-related species live in similar habitats, yet under quite different conditions, which provided an opportunity to investigate how similar types of habitats influence patterns of distribution, abundance and size-structure in intertidal versus subtidal environments. For each species, there were similar associations between biogenically structured habitat and densities. The intertidal species, Turbo undulates, were more abundant, with greater proportions of small individuals in habitats formed by the canopy-forming alga, Hormosira banksii, the solitary ascidian, Pyura stolonifera or the turfing red alga, Corallina officinalis compared to simple habitat (bare rock). Similarly, more Turbo torquatus were found in biogenically structured subtidal habitat, i.e. canopy-forming algae, Ecklonia radiata, mixed algal communities (‘fringe’), or turfing red algae (Corallina officinalis and Amphiroa aniceps) than where habitat is simple (barrens). Small T. torquatus were more abundant in areas of turf and ‘fringe’, while large snails were more abundant in areas of kelp and barrens. These patterns were found at each location sampled (i.e. eight intertidal and two subtidal rocky reefs) and at all times of sampling, across each environment. This study highlighted the consistent influence of biogenically structured habitats on the distribution, abundance and size-structure of intertidal and subtidal turban snails and forms a basis for increasing the understanding of the potential underlying processes causing such patterns.
Highlights
Patchiness of habitat has important influences on distributions and abundances of organisms that live in a mosaic with different habitats of varying structure and composition [1,2,3,4]
Eight intertidal rocky shores (Figure 1; NSW Fisheries research permit F96/146-6.0) were selected where T. undulatus were abundant (.10 per 0.25 m2) and the distribution of biogenically structured habitats was patchy, i.e. there were areas of homogeneous structured habitats interspersed with unstructured habitats
Many studies have shown the importance of structurallycomplex biogenic habitats on intertidal or subtidal rocky reefs, for example beds of algae (e.g. [40,46,47]), as influences on smallscale patterns of distribution of a diverse array of taxa
Summary
Patchiness of habitat has important influences on distributions and abundances of organisms that live in a mosaic with different habitats of varying structure and composition [1,2,3,4]. Knowledge of how organisms are distributed in relation to spatial heterogeneity of their environment is fundamental to ecology and has been of concern for many decades (see references in [3]). Despite there being numerous studies done to investigate influences of environmental heterogeneity on a single species in different types of habitat, there have been relatively few comparative tests of such research in different types of habitats for similar species, or among different species across similar types of habitats Ecology has been criticised for its lack of progress because of the lack of general ecological models that researchers need to be able to make accurate predictions under changing environmental conditions [13,14,15,16]. In the absence of general predictive models, there cannot be full understanding about ecological requirements of organisms, nor the types of habitats with which they are associated [12,14,15,16,17,18,19,20]
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